Glass-ceramic composition for recording disk substrate

ABSTRACT

A glass ceramics composition for recording disk substrate contains, essentially, expressed in terms of weight percent on the oxide basis, from 54.5 to 59.5 wt % of SiO 2 , from 10 to 30 wt % of Al 2 O 3 , from 10 to 30 wt % of MgO, and from 3 to 12 wt % of Li 2 O.

RELATED APPLICATION

This application is based on application No. 11-200443 filed in Japan,the content of which is hereby incorporated by reference.

1. Field of the Invention

The present invention relates to a glass ceramic composition, moreparticularly, relates to the glass ceramic composition suitable formagnetic disk substrate.

2. Description of the Prior Art

Magnetic disks are mainly used as recording media of computers. Aluminumalloys have heretofore been used as the material of magnetic disksubstrates. However, in the recent trend for a smaller size, a thinnerthickness, and a higher recording density of magnetic disks, a highersurface flatness and a higher surface smoothness are increasinglydesired. Aluminum alloys cannot satisfy the desire, and a material formagnetic disk substrates which can replace aluminum alloys is required.Thus, in particular, recent attention has been focused on the glasssubstrate for the disk because of its surface flatness and smoothnessand excellent mechanical strength.

As glass substrates for disks for recording media, there have beenproposed a chemically reinforced glass substrate having a surfacereinforced by ion exchange or like method and a glass ceramics substrateon which a crystal component has been precipitated to reinforce thebonding. In recent years, the latter crystallized glass substrate inwhich a crystallite has been precipitated in glass by heat treatment hasdrawn particular attention because of its excellent strength and highproductivity.

As recent requirements on the performance of a disk for a recordingmedium have been more stringent, a substrate material has also beenrequired to have an increased strength related directly to the bendingor warping of the disk during high-speed rotation. The strength can berepresented by the elastic modulus ratio (=) Young's modulus/specificgravity) of the substrate material. The elastic modulus ratio having ahigher value indicates a higher mechanical strength. However, aglass-ceramics composition conventionally known has the problem that theproductivity thereof is reduced significantly if the strength thereof isto be increased.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a glass ceramiccomposition which is suitable for use in an improved glass substrate fora recording medium.

Another object of the present invention is to provide a glass ceramiccomposition which has high productivity irrespective of its high elasticmodulus ratio.

Still another object of the present invention is to provide a disksubstrate for a recording medium which has high productivityirrespective of its high elastic modulus ratio.

Thus, the present invention provides a glass-ceramics compositionconsisting essentially, expressed in terms of weight percent on theoxide basis, of, from 54.5 to 59.5 wt % of SiO₂, from 10 to 30 wt % ofAl₂O₃, from 10 to 30 wt % of MgO, and from 3 to 12 wt % of Li₂O.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a glass-ceramics composition consistingessentially, expressed in terms of weight percent on the oxide basis,of, from 54.5 to 59.5 wt % of SiO₂, from 10 to 30 wt % of Al₂O₃, from 10to 30 wt % of MgO, and from 3 to 12 wt % of Li₂O.

In the composition, SiO₂ is a glass network former oxide. The meltingproperties deteriorate if the proportion thereof is lower than 54.5 wt%. If the proportion thereof exceeds 59.5 wt %, the composition becomesstable as glass so that the crystal is less likely to be precipitated.

Al₂O₃ is a glass intermediate oxide and a component of an aluminumborate crystal, which is a crystalline phase precipitated by heattreatment. If the proportion of Al₂O₃ is lower than 10 wt %, the crystalis precipitated in reduced quantity and a sufficient strength is notachieved. If the composition rate of Al₂O₃ exceeds 30 wt %, the meltingtemperature is increased and devitrification is more likely to occur.

MgO is a fluxing agent. MgO forms an aggregation of crystal grains. Ifthe proportion of MgO is lower than 10 wt %, the range of operatingtemperatures is narrowed down and the chemical durability of a glassmatrix phase is not improved. If the proportion of MgO exceeds 30%,another crystalline phase is precipitated so that it becomes difficultto achieve a desired strength.

Li₂O is a fluxing agent. By adding Li₂O serving as a fluxing agent,production stability has been improved. If the proportion of Li₂O islower than 3 wt %, the melting properties deteriorate. If the proportionof Li₂O exceeds 12 wt %, stability in the polishing to cleaning steps isdegraded.

Besides the above-mentioned basic components, P₂O₅ as a fluxing agentand a nuclear forming agent can been added. By adding P₂O₅ is a fluxingagent and a nuclear forming agent for precipitating a silicate crystal,the crystal are uniformly precipitated over the entire glass. If theproportion of P₂O₅ is lower than 0.1 wt %, satisfactory nuclei are lesslikely to be formed so that crystal grains are increased in size or thecrystal is precipitated non-uniformly. Consequently, an extremely smalland uniform crystal structure is less likely to be obtained and a flat,smooth surface required of the glass substrate as a disk substratecannot be obtained by polishing. If the proportion of P₂O₅ exceeds 5 wt%, the reactivity of the glass in a molten state to a filter medium isincreased and the devitrifiability thereof is also increased, so thatproductivity during melt molding is reduced. In addition, the chemicaldurability is reduced, which may affect a magnetic film, while thestability in the polishing to cleaning steps is lowered.

Besides the above-mentioned basic components, Nb₂O₅ as a fluxing agentcan been added. By adding Nb₂O₅ serving as a fluxing agent, productionstability has been improved. If the proportion of Nb₂O₅ is lower than0.1 wt %, the rigidity is not sufficiently improved. If the proportionof Nb₂O₅ exceeds 9 wt %, the crystallization of the glass becomesunstable and the precipitated crystalline phase cannot be controlled, sothat desired characteristics are less likely to be obtained.

Besides the above-mentioned basic components, Ta₂O₅ as a fluxing agentcan been added. By adding Ta₂O₅ serving as a fluxing agent, the meltingproperties and strength are improved, while the chemical durability ofthe glass matrix phase is improved. If the proportion of Ta₂O₅ is lowerthan 0.1 wt %, however, the rigidity is not sufficiently improved. Ifthe proportion of Ta₂O₅ exceeds 9 wt %, the crystallization of the glassbecomes unstable and the precipitated crystalline phase cannot becontrolled, so that desired characteristics are less likely to beobtained.

Besides the above-mentioned basic components, TiO₂ as a fluxing agentcan been added. By adding TiO₂ serving as a fluxing agent has beenadded, production stability has been improved. If the proportion of TiO₂is lower than 0.1 wt %, the melting properties deteriorate and thecrystal is less likely to grow. If the proportion of TiO₂ exceeds 12 wt%, the crystallization is promoted rapidly so that the control of thecrystallized state becomes difficult, the precipitated crystal isincreased in size, and the crystalline phase becomes non-uniform. Thisprevents the obtention of an extremely small and uniform crystalstructure and the obtention of a flat, smooth surface by polishing,which is required of the glass substrate as a disk substrate. Moreover,devitrification is more likely to occur during melt molding, whichlowers productivity.

Besides the above-mentioned basic components, ZrO₂ as a glass modifyingoxide can been added. By adding ZrO₂ serving as a glass modifying oxide,a glass nucleating agent functions effectively. If the proportion ofZrO₂ is lower than 0.1 wt %, satisfactory crystal nuclei are less likelyto be formed so that crystal grains are increased in size and thecrystal is precipitated non-uniformly. This prevents the obtention of anextremely small and uniform crystal structure and the obtention of aflat, smooth surface by polishing, which is required of the glasssubstrate as a disk substrate. In addition, the chemical durability andthe migration resistance are reduced. This may affect a magnetic filmand degrades stability in the polishing to cleaning steps. If theproportion of ZrO₂ exceeds 12 wt %, the melting temperature is increasedand devitrification is more likely to occur during melt molding, whichlowers productivity. Moreover, the precipitated crystalline phasechanges so that desired characteristics are less likely to be obtained.

Besides the above-mentioned basic components, B₂O₃ as a former can beenadded. By adding B₂O₃ serving as a former, the phase splitting of theglass is promoted and the precipitation and growth of the crystal arcpromoted. If the proportion of B₂O₃ is lower than 0.1 wt %, the meltingproperties are not improved sufficiently. If the proportion of B₂O₃exceeds 5 wt %, devitrification is more likely to occur and moldingbecomes difficult, while the crystal is increased in size, so that anextremely small crystal is no more obtained.

Besides the above-mentioned basic components, Y₂O₃ as a fluxing agentcan been added. By adding Y₂O₃ serving as a fluxing agent, the rigidityhas been improved. If the proportion of Y₂O₃ is lower than 0.1 wt %,however, the rigidity is not improved sufficiently. If the proportion ofY₂O₃ exceeds 9 wt %, the precipitation of the crystal is suppressed anda sufficient degree of crystallization is not achieved, so that desiredcharacteristics are not achieved.

Besides the above-mentioned basic components, K₂O as a fluxing agent canbeen added. By adding K₂O serving as a fluxing agent, productionstability has been improved. If the proportion of K₂O is lower than 0.1wt %, however, the melting properties are not improved sufficiently. Ifthe proportion of K₂O exceeds 5 wt %, the glass becomes stable and thecrystallization is suppressed, while the chemical durability is reduced.This may affect a magnetic film and degrades stability in the polishingto cleaning steps.

Besides the above-mentioned basic components, Sb₂O₃ as a clarifier canbeen added. By adding Sb₂O₃ serving as a clarifier, production stabilityhas been improved. If the proportion of Sb₂O₃ is lower than 0.1 wt %,however, a sufficient clarifying effect can not be achieved andproductivity is lowered. If the proportion of Sb₂O₃ exceeds 5 wt %, thecrystallization of the glass becomes unstable and the precipitatedcrystalline phase cannot be controlled so that required characteristicsare less likely to be obtained.

Besides the above-mentioned basic components, ZnO as a fluxing agent canbeen added. By adding ZnO serving as a fluxing agent, it helps uniformprecipitation of the crystal. If the proportion of ZnO is lower than 0.1wt %, however, the uniformity of the crystal is not sufficientlyimproved. If the proportion of ZnO exceeds 5 wt %, the glass becomesstable and the crystallization is suppressed, so that required strengthis less likely to be achieved.

Besides the above-mentioned basic components, La₂O₃ as a fluxing agentcan been added. By adding La₂O₃ serving as a fluxing agent, theprecipitation of the crystal is suppressed. If the proportion of La₂O₃is lower than 0.1 wt %, however, the rigidity is not improvedsufficiently. If the proportion of La₂O₃ exceeds 5 wt %, thecrystallization of the glass becomes unstable and the precipitatedcrystalline phase cannot be controlled, so that required properties areless likely to be obtained.

Next, a description will be given to a fabrication method. Raw materialscontaining the main components of the glass substrate to be finallyproduced are sufficiently mixed in specified proportions. The resultingmixture is placed in a platinum crucible and caused to melt. The moltenproduct is cast in a metal mold so that it is formed into a roughconfiguration and annealed to a room temperature. The molten product isthen held at a specified temperature for a specified time during aprimary treatment (heat treatment) such that crystal nuclei are formed.Subsequently, the molded mixture is held at a specified temperature fora specified time during a secondary heat treatment such that crystalnuclei grow. By slowly cooling the molded mixture, an objectivecrystallized glass is obtained.

NUMERIC EXAMPLES

A description will be given next to specific numerical examplesincorporating the embodiments. In TABLE 1 are shown: theproportions(unit: wt %) of materials composing the glasses of the firstto fifth examples; the melting temperatures and times; the primary heattreatment temperatures and times; the secondary heat treatmenttemperatures and times; the main precipitated crystalline phases; thesubordinate precipitated crystalline phases; the mean diameters of thecrystal grains; the specific gravity s: the Young's moduli; and thespecific moduli. Likewise, the glasses of the sixth to tenth examplesare shown in TABLE 2. Likewise, the glasses of the eleventh to fifteenthexamples are shown in TABLE 3. Likewise, the glasses of the sixteenth totwentieth examples are shown in TABLE 4.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 SiO₂ 54.5 54.958.0 55.0 57.2 Al₂O₃ 18.1 13.7 18.0 19.2 26.5 MgO 11.2 11.5 20.7 17.911.2 P₂O₅ 2.0 1.6 0.2 1.2 Nb₂O₅ 2.0 Ta₂O₅ Li₂O 3.0 5.1 3.1 6.7 3.1 TiO₂6.9 7.4 ZrO₂ B₂O₃ Y₂O₃ 3.7 K₂O 1.7 Sb₂O₃ 0.3 0.4 ZnO La₂O₃ MeltingTemperature (° C.) 1200 1200 1250 1250 1250 Melting Time (hours) 3.503.50 4.00 4.00 4.00 Primary Treatment Temperature (° C.) 640 670 670 670670 Primary Treatment Time (hours) 5.00 5.00 5.50 5.50 5.50 SecondaryTreatment Temperature (° C.) 710 730 730 730 730 Secondary TreatmentTime (hours) 4.50 4.50 5.00 5.00 5.00 Main Crystalline Phase MagnesiumMagnesium Magnesium Magnesium Magnesium alumina silicate aluminasilicate alumina silicate alumina silicate alumina silicate SubCrystalline Phase Rutil Rutil Diameter of Crystal 0.05 0.05 0.05 0.050.05 Specific Gravity (g/cm³) 2.64 2.66 2.68 2.62 2.74 Yong's Modulus95.40 96.20 98.40 93.40 98.40 Elastic Modulus Ratio 36.12 36.21 36.7035.64 35.90

TABLE 2 Example 6 Example 7 Example 8 Example 9 Example 10 SiO₂ 54.654.8 58.4 54.7 58.0 Al₂O₃ 16.9 15.6 15.0 28.0 15.7 MgO 16.0 24.0 16.214.3 20.3 P₂O₅ Nb₂O₅ 4.0 Ta₂O₅ 2.2 5.2 Li₂O 8.5 3.4 5.2 3.0 6.0 TiO₂ZrO₂ B₂O₃ Y₂O₃ K₂O Sb₂O₃ ZnO La₂O₃ Melting Temperature (° C.) 1250 12501250 1250 1250 Melting Time (hours) 4.00 4.00 4.00 4.00 4.00 PrimaryTreatment Temperature (° C.) 670 670 670 670 670 Primary Treatment Time(hours) 5.50 5.50 5.50 5.50 5.50 Secondary Treatment Temperature (° C.)730 730 730 730 730 Secondary Treatment Time (hours) 5.00 5.00 5.00 5.005.00 Main Crystalline Phase Magnesium Magnesium Magnesium MagnesiumMagnesium alumina silicate alumina silicate alumina silicate aluminasilicate alumina silicate Sub Crystalline Phase Diameter of Crystal 0.050.05 0.05 0.05 0.05 Specific Gravity (g/cm³) 2.76 2.79 2.76 2.68 2.72Yong's Modulus 100.40 100.40 103.40 107.40 105.40 Elastic Modulus Ratio36.36 35.97 37.45 40.06 38.74

TABLE 3 Example 11 Example 12 Example 13 Example 14 Example 15 SiO₂ 54.959.0 55.2 58.4 54.6 Al₂O₃ 19.2 16.1 21.0 18.8 20.0 MgO 18.4 10.5 20.212.2 21.6 P₂O₅ Nb₂O₅ Ta₂O₅ Li₂O 3.5 5.4 3.1 6.4 3.3 TiO₂ 4.0 9.0 ZrO₂0.5 4.2 B₂O₃ 0.5 Y₂O₃ K₂O Sb₂O₃ ZnO La₂O₃ Melting Temperature (° C.)1250 1250 1250 1250 1200 Melting Time (hours) 4.00 4.00 4.00 4.00 3.50Primary Treatment Temperature (° C.) 670 670 670 670 640 PrimaryTreatment Time (hours) 5.50 5.50 5.50 5.50 5.00 Secondary TreatmentTemperature (° C.) 730 730 730 730 710 Secondary Treatment Time (hours)5.00 5.00 5.00 5.00 4.50 Main Crystalline Phase Magnesium MagnesiumMagnesium Magnesium Magnesium alumina silicate alumina silicate aluminasilicate alumina silicate alumina silicate Sub Crystalline Phase RutilRutil Diameter of Crystal 0.05 0.05 0.05 0.05 0.05 Specific Gravity(g/cm³) 2.96 2.99 2.89 2.92 2.64 Yong's Modulus 108.60 107.60 103.40103.60 95.40 Elastic Modulus Ratio 36.68 35.97 35.77 35.47 36.12

TABLE 4 Example 16 Example 17 Example 18 Example 19 Example 20 SiO₂ 56.256.2 58.5 54.5 59.0 Al₂O₃ 20.4 22.6 12.0 20.0 11.2 MgO 16.0 16.2 20.118.5 15.3 P₂O₅ Nb₂O₅ Ta₂O₅ Li₂O 4.2 3.2 5.2 3.3 4.0 TiO₂ ZrO₂ B₂O₃ 3.2Y₂O₃ 1.8 4.2 K₂O 1.0 4.0 Sb₂O₃ 0.2 2.0 ZnO 0.5 2.0 La₂O₃ 2.0 2.5 MeltingTemperature (° C.) 1200 1250 1250 1200 1200 Melting Time (hours) 3.504.00 4.00 4.00 4.00 Primary Treatment Temperature (° C.) 640 670 670 640640 Primary Treatment Time (hours) 5.00 5.50 5.50 5.50 5.50 SecondaryTreatment Temperature (° C.) 710 730 730 710 710 Secondary TreatmentTime (hours) 4.50 5.00 5.00 5.00 5.00 Main Crystalline Phase MagnesiumMagnesium Magnesium Magnesium Magnesium alumina silicate aluminasilicate alumina silicate alumina silicate alumina silicate SubCrystalline Phase Diameter of Crystal 0.05 0.05 0.05 0.05 0.05 SpecificGravity (g/cm³) 2.64 2.92 2.96 2.96 2.99 Yong's Module 95.40 109.40111.40 102.40 105.40 Elastic Module Ratio 36.12 37.45 37.62 34.58 35.24

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodification depart from the scope of the present invention, they shouldbe construed as being included therein.

What is claimed is:
 1. A glass ceramics composition for recording disk substrate consisting essentially, expressed in terms of weight percent on an oxide basis, of from 54.5 to 59.5 wt % of SiO₂, from 10 to 30 wt % of Al₂O₃, from 10 to 30 wt % of MgO, and from 3 to 12 wt % of Li₂O.
 2. A glass ceramics composition as claimed in claim 1, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 5 wt % of P₂O₅.
 3. A glass ceramics composition as claimed in claim 1, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 9 wt % of Nb₂O₅.
 4. A glass ceramics composition as claimed in claim 1, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 9 wt % of Ta₂O₅.
 5. A glass ceramics composition as claimed in claim 1, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 12 wt % of TiO₂.
 6. A glass ceramics composition as claimed in claim 1, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 12 wt % of ZrO₂.
 7. A glass ceramics composition as claimed in claim 1, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 5 wt % of B₂O₃.
 8. A glass ceramics composition as claimed in claim 1, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 5 wt % of K₂O.
 9. A glass ceramics composition as claimed in claim 1, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 5 wt % of Sb₂O₃.
 10. A glass ceramics composition as claimed in claim 1, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 5 wt % of ZnO.
 11. A glass ceramics composition as claimed in claim 1, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 5 wt % of La₂O₃.
 12. A glass ceramic recording disk substrate, wherein the glass ceramic is prepared from a composition which consists essentially, expressed in terms of weight percent on an oxide basis, of from 54.5 to 59.5 wt % of SiO₂, from 10 to 30 wt % of Al₂O₃, from 10 to 30 wt % of MgO, and from 3 to 12 wt % of Li₂O.
 13. A recording disk substrate as claimed in claim 12, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 5 wt % of P₂O₅.
 14. A recording disk substrate as claimed in claim 12, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 9 wt % of Nb₂O₅.
 15. A recording disk substrate as claimed in claim 12, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 9 wt % of Ta₂O₅.
 16. A recording disk substrate as claimed in claim 12, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 12 wt % of TiO₂.
 17. A recording disk substrate as claimed in claim 12, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 12 wt % of ZrO₂.
 18. A recording disk substrate as claimed in claim 12, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 5 wt % of B₂O₃.
 19. A recording disk substrate as claimed in claim 12, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 5 wt % of K₂O.
 20. A recording disk substrate as claimed in claim 12, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 5 wt % of Sb₂O₃.
 21. A recording disk substrate as claimed in claim 12, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 5 wt % of ZnO.
 22. A recording disk substrate as claimed in claim 12, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 5 wt % of La₂O₃.
 23. A glass ceramics composition as claimed in claim 1, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 9 wt % Y₂O₃.
 24. A recording disk substrate as claimed in claim 12, wherein said glass ceramic composition further consists essentially, expressed in terms of weight percent on an oxide basis, of from 0.1 to 9 wt % of Y₂O₃. 